1. Field of the Invention
The present invention relates to an optical measuring device of a scanning type that uses a collimated beam.
2. Description of the Related Art
An optical measuring device comprises a projector and a photoreceptor located separately by a scan region in which a work to be measured locates. A collimated beam from the projector is employed to repeatedly scan the scan region and the photoreceptor receives the beam transmitted through the scan region to generate scanned signals. The scanned signals are specifically processed to indicate a measured value (such as a dimension and roundness of the work to be measured).
The projector and the photoreceptor contain expensive optical components (such as a semiconductor laser, photodiodes, lenses and mirrors). To prevent contamination of and damage to the optical components, the projector and the photoreceptor are each provided with a cabinet that houses the optical components.
The cabinet has a window with a protective glass fitted therein. The collimated beam generated at the projector is led to the scan region in an external ambient after it transmits through the protective glass. The collimated beam transmitted through the scan region transmits through the protective glass and is led into the photoreceptor. The protective glass is exposed to the external ambient and accordingly easily contaminated and may be damaged occasionally. The contamination, for example, becomes an obstacle on measurements and cause increased measurement errors. A dimension-measuring device has therefore been proposed that can detect a foreign substance located on the optical path of the beam (JP-A11-83448, Paragraphs 0029-0043, FIGS. 2 and 3).
The present invention has an object to provide an optical measuring device capable of improving the precision of detection of an abnormality on the optical path of the beam.